When making long-term investments, you need to look for companies with longevity. Pay attention not only to the buzz surrounding a company's stock, but also to the company's ability to stay in business for a long time. 

Two key factors in determining staying power are timeliness and demand. These factors work together because the best time to launch a new product or service is when the demand for what is offered is high. Age-old companies have mastered catering to the needs of the clients, building trust and confidence in the average consumer and investors. Explosive start-up companies tend to focus on innovation, making them more inclined to jump on opportunities to create the next best thing that will meet the demand of their customers. From rare artifacts of historical significance to technology that makes life more efficient, being able to cater to the wants and needs of customers with the highest levels of efficiency and adaptability is what really determines a company's staying power.

Old money
The oldest company on the New York Stock Exchange is Sotheby's (BID). If you have an appreciation for fine art, wine, and jewelry -- or at least the prices these luxuries can command -- then consider investing in this luxury auctioneer. Founded in London in 1744, Sotheby's is a prime example of being the first and the finest. It began with the auctioning of "scarce and valuable" books. From then on, the company expanded to include rare works of art, Napoleon's St. Helena library, fine jewelry, and more. 

Sotheby's hand-picks the finest wines through personal tasting and selects the most precious diamonds via its partnership with Steinmetz Diamond Group. All of these offerings help to create the ultimate one-stop-shop experience for the affluent art investor who enjoys a life of luxury. Further, Sotheby's auction platform has evolved to meet 21st-century standards by allowing clients to place bids online in real time via an online tool called BIDnow.

Sotheby's shares went for $6.96 apiece when the company hit the market in 1988. Today, shares have reached about $47. That's a 570%-plus increase in value, meaning mega earnings for the early investor!

New money
Electric-vehicle manufacturer Tesla Motors (TSLA -0.08%) is a company founded with sustainability in mind. CEO Elon Musk is dedicated to moving society toward sustainable energy sources; in fact, no one can question his progressive street cred. He's a shareholder and co-creator of major U.S. solar-power company SolarCity, and he sits on the boards of various space, aeronautics, and engineering foundations and societies as well. He created the Musk Foundation, which focuses on aerospace, clean energy, science education, and pediatric health. He is also a trustee of the X Foundation, which promotes renewable-energy technologies.

This forward thinking and genuine concern for mankind's future is what makes Tesla Motors a company with staying power.

With its flagship Model S vehicle and rapidly spreading Supercharger battery-charging stations, Tesla Motors is only beginning to show its true promise as a long-term investment.

Source: iRobot.

Another company to keep your eye in for the long term is iRobot (IRBT 1.06%). Remember the Jetsons? Remember the robot that did all the house work and even kept the humans apprised of important information? That robot is slowly making its way into our everyday lives, and this is why iRobot and its innovative, visionary products have staying power.

iRobot's home vacuum cleaner robot was only the beginning for its venture into technology that makes home life more efficient, and as the robots expand into defense and security, hospitals, retail, and more, the possibilities become endless. For example, iRobot is currently developing a prototype of what it calls "one of the world's most advanced mobile robotics platforms." The robot, named Ava, is set to improve human-robot interactions with an advanced self-navigating platform that will help it detect and avoid humans and objects. It will integrate touch, voice, and gesture control through a tablet-device interface and link with technological advancements in artificial intelligence, WiFi connectivity, and power efficiency. 

The company has also launched it's educational program, STEM (science, technology, engineering and math). This program aims to introduce students of all ages to the wonders of the robotics industry, offering classroom visits, mentoring, and internships to encourage students to advance their interests in science, engineering, and careers in the robotics industry. 

In its six years on the market, iRobot's share price has increased only 20%; however, although the stock lagged considerably before the recession, it's up 455% since the economy hit bottom, far outpacing the market. The company saw 20% growth in home robot business in 2013 and is expecting nothing but more growth -- around 14% -- for 2014. 

Open your mind when choosing companies to invest in. Are there any problems in this world that need to be solved? Are there any companies providing solutions? Keep these questions in mind when looking for long-term investments, and you will find companies that not only have staying power but will also make you proud to be a part-owner.